19-Nor-vitamin D compounds are vitamin D analogs in which the ring A exocyclic methylene group (carbon 19) typical of all vitamin D compounds has been removed and replaced by two hydrogen atoms. Specifically, these compounds exhibit a selective activity profile with high potency in inducing cellular differentiation, and minimal bone calcification activity. Such a differential activity profile renders these compounds useful for the treatment of malignancies, or the treatment of various skin disorders. Two different methods of synthesis of these 19-nor-vitamin D analogs have been described (Perlman et al. Tetrahedron Letters 31, 1823 (1990); Perlman et al. Tetrahedron Letters 32, 7663 (1991), and DeLuca et al., U.S. Pat. No. 5,086,191).
A new method for the synthesis of such analogs has now been developed and is disclosed herein. The method takes advantage of the finding of Walborsky and Wust (J. Am. Chem. Soc. 104, 5807, 1982) that 1,4-diol-2-ene compounds can be reduced by low-valent titanium reagents to 1,3-dienes. Solladie and Hutt (J. Org. Chem. 52, 3560, 1987) have exploited this type of reduction for the preparation of dihydrotachysterol and dihydrovitamin D compounds.